Truck mounted brake assemblies are well known in the railway industry. These brake assemblies have several desirable qualities which makes them very popular with railway vehicle manufacturers. One type of a truck mounted brake assembly is one which is commonly referred to in the railway industry as a WABCOPAC.RTM. braking system (WABCOPAC.RTM. is a registered trademark to Westinghouse Airbrake Company, the assignee of the present invention) This truck mounted braking system typically comprises a pair of brake beams, having brake heads secured at the ends thereof, separated by a pair of brake cylinders. This system permits direct application of brake cylinder force to the brake shoes.
Another type of known truck mounted braking system is one which is commonly referred to as a TMX.RTM. truck mounted braking system (TMX.RTM. is a registered trademark to Westinghouse Airbrake Company, the assignee of the present invention). The TMX.RTM. truck mounted braking system has several desirable qualities which also makes this system popular with railway vehicle manufacturers. The most significant of these qualities are that these brake assemblies are formed of highly durable, lightweight material and utilize a single brake cylinder providing a significant weight reduction per carset. Another quality of these brake assemblies is that they are easy to install and adjust, require no special bolsters or connections for this installation, readily fit all standard trucks with combination bolsters and allow for simplified replacement of the brake heads. Another significant advantage of the TMX.RTM. truck mounted brake assembly is that the arrangement of the components within the brake assembly, including the use of a double-jaw slack adjuster, allows for a more even brake shoe wear than previously used types of braking systems.
Various other types of truck mounted braking systems are well known in the railway industry. The common characteristic of these currently used truck mounted braking systems in the U.S. railway industry is that the truck side frames are fixed to the wheel and axle and consequently, the truck mounted braking system is secured to the truck side frame. This type of mounting of the braking system subjects the braking system to a significant amount of shock as the railway vehicle moves along a route. Additionally, due to this type of mounting, occasionally, full contact is not made between the brake shoes and the wheels as the car moves up and down.
This differs from the European railway industry wherein the bolster and side frame move with the body. Thus, in the European market, presently used braking systems are suspended within the truck arrangement so that the braking system becomes part of the sprung system of the vehicle, giving the braking system more cushion and preventing shock onto the system.
A significant drawback to the systems currently in use in the European market is that these braking systems require the use of an individual brake unit at each wheel, significantly increasing the cost of the braking system and the cost of maintaining each of these individual units. Another disadvantage is that the use of an individual braking unit at each wheel significantly increases the weight of the carsets, as well as, the energy required to power the railway vehicle.